1. Field of the Invention
The present invention relates to an in-line mixing apparatus, a process for mixing reactive chemical solutions using the apparatus, and a process for producing microcapsules. More particularly, the present invention relates to an improvement of a technique of mixing raw material chemical solutions for a coating solution of pressure-sensitive duplicating paper utilizing microcapsules.
The invention also relates to an in-line mixing apparatus and a process for producing microcapsules, and more particularly, to an improvement of a technique of mixing reactive chemical solutions in an in-line mixing apparatus having a mechanical seal for sealing a rotation shaft of a rotary blade.
2. Description of the Related Art
In the production of pressure-sensitive paper, heat-sensitive paper, a photographic photosensitive material, cosmetics, a paint or the like by utilizing microcapsules, the following procedures are widely employed. A chemical solution containing a polyvalent isocyanate is added to an oil phase solution in which a solute which is to be a core substance of capsules is dissolved in advance, and these are mixed in an in-line mixing apparatus. A water phase solution is then added to the mixed chemical solution, and an oil-in-water emulsion is prepared by agitation. A suitable auxiliary additive, such as a polyvalent amine, is added to the emulsion, and the mixture is subjected to a suitable operation, such as heating, whereby microcapsules having a film, such as a film of polyurethane or polyurea, are prepared. The procedures are described, for example, in Japanese Patent Application Laid-Open (JP-A) No. 5-57178.
In this series of operations, an in-line mixing apparatus is used as the mixing apparatus for mixing the oil phase solution with the chemical solution such as a polyvalent isocyanate to achieve a high throughput in an in-line mixing process over a long period of time, as described in JP-A No. 5-57178. As the in-line mixing apparatus, an in-line mixer can be used, such as a high shearing mixer, a pipeline homo-mixer, a homo-mix line-flow or a fine flow mill.
In the case where a chemical solution of a polyvalent isocyanate and a polyol that reacts with the polyvalent isocyanate is continuously added to and continuously mixed with an oil phase solution that serves as a process fluid, an extremely hard reaction product having a blackish-brown color is formed in an agitation flow path of the in-line mixing apparatus. The reaction product thus formed adheres to and develops on a shaft seal or mechanical seal of a rotation shaft for supporting agitation blades provided in the agitation flow path. Consequently, the function of the shaft sealing portion or mechanical seal is deteriorated, causing such problems as leakage of the liquid from the shaft sealing portion or mechanical seal.
Furthermore, water, which is contained in the oil phase in trace amounts, reacts with the polyvalent isocyanate, and the resultant reaction product adheres to and develops on the shaft sealing portion or mechanical seal of the rotation shaft supporting agitation blades provided in the mixing flow path, so that the function of the shaft sealing portion or mechanical seal is deteriorated, causing such problems as leakage of the liquid from the shaft sealing portion or mechanical seal.
Particularly, in the case where the shaft sealing portion is a mechanical seal, when the reaction product is adhered on a pressing means for pressing a seal ring member to a rotation ring member, the pressing means cannot conform with vibrations caused by high speed rotation of the rotation ring member, and the pressing pressure of the seal ring member to the rotation ring member is decreased, causing leakage of the liquid.
Due to the problems described above, stable operation over a long period of time, which is an intrinsic advantage of continuous mixing by the in-line mixing apparatus, becomes difficult to carry out, and operation shutdown and disassembly for cleaning are necessary after an extremely short period of time. Thus, a considerable reduction in production efficiency is caused.